Hi Helmut,
ANAN-100D provides two phase-coherent receivers in one USD$3500 box, along
with a 100W transmitter. The cost is why I didn't bother mentioning it. But
obviously we can make a dual SDR receiver for a lot less. Are there any
other off-the-shelf hardware solutions today? I have a Hermes and three
USRP's on hand, and might also like to experiment with up-conversion for
Katena (formerly Whitebox) when we have dealt with higher-priority issues.
Thanks
Bruce
On Sun, Sep 6, 2015 at 1:57 PM, Helmut <dc...@gmx.de> wrote:
> Polarization diversity is another approach to minimize selective fading we
> have on the to do list. Our HPSDR environment provides excellent diversity
> performance.
>
>
>
> 73, Helmut, DC6NY
>
>
>
> *Von:* Bruce Perens [mailto:br...@perens.com]
> *Gesendet:* Sonntag, 6. September 2015 21:44
> *An:* freetel-codec2@lists.sourceforge.net
> *Betreff:* Re: [Freetel-codec2] Smoothing the digital cliff (4+4 QAM
> bitrate peeling idea)
>
>
>
> Any graceful degradation scheme should take into account that the main
> problem we face is frequency-selective attenuation due to fading. The
> mechanism, I am told, is multiple depths of reflection from the ionosphere
> leading to multiple phases combined at the antenna. There is a lot of
> literature saying that one can actually reduce the fading with circular
> receive antenna polarization. I've not gotten to test it.
>
>
>
> If you plan to make this work with conventional antennas, you can
> experiment with carrier spacing on the theory that some number of carriers
> would not be in a fade at one time.
>
>
>
> Thanks
>
>
>
> Bruce
>
>
>
> On Sun, Sep 6, 2015 at 9:01 AM, Tomas Härdin <tjop...@acc.umu.se> wrote:
>
> Hi
>
> (I tried sending this a few days ago but forgot to confirm my
> subscription to this list - oops! So resending)
>
> My name is Tomas and I've been following the development of codec2 on
> and off for a few years now, and since getting my ham license earlier
> this year I find myself thinking about it more. A few days ago I had
> what I thought was a clever idea for fixing the "digital cliff" problem
> Mike mentioned in a talk that's up on YouTube (I forget which). Today I
> see on the roadmap post[1] that this is currently being worked on using
> two GMSK streams, but I thought "hey, maybe someone will find it
> interesting". So here goes:
>
> The idea assumes that codec2 can make use of bitrate peeling. That is,
> that we can split the stream up into two or more streams where the first
> one provides a rough but usable quality, and subsequent streams improve
> upon this. H.264's SVC would be an example from the video world
>
> So the idea is take these streams and modulate them onto a hierarchical
> QAM system. The simplest would be to take the current FDMDV modem and
> instead of using 14x QPSK (aka 4-QAM) carriers you use 7x 16-QAM
> carriers. You then code the more important bitstream into the most
> significant bits in each 16-QAM symbol, and the improvement stream into
> the lower bits (assuming the two streams have identical bitrate). Since
> you now have half the number of carriers you can put twice the amount of
> power into each carrier
>
> That's about it. Lots of variants are of course possible, but this
> should get the point across. I may experiment with the idea once I get
> some suitable SSB equipment, but for now I'm interested in feedback even
> if it's just shooting it down :)
>
> /Tomas, SA2TMS
>
> [1] http://www.rowetel.com/blog/?p=3931
>
>
>
>
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